在KITKAT上"onActivityResult"有时为空值的Android变量

Question

private void openCamera(int imageArray){
Intent cameraIntent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
fileUri = Uri.fromFile(new File(Environment.getExternalStorageDirectory()+"/SurveyDA/assets/images","absen_" +
System.currentTimeMillis() + ".jpg"));
Log.d("ddddd : ", String.valueOf(fileUri));
cameraIntent.putExtra(android.provider.MediaStore.EXTRA_OUTPUT, fileUri);
startActivityForResult(cameraIntent, imageArray);
}

当我想打开相机时，我设置了文件uri，日志成功返回uri

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == RESULT_OK) {
try {
//getting bitmap object from uri
Log.d("ddddd : ", String.valueOf(fileUri));
bitmapImage[requestCode] = MediaStore.Images.Media.getBitmap(this.getContentResolver(), fileUri);
// Initialize a new ByteArrayStream
ByteArrayOutputStream stream = new ByteArrayOutputStream();
// Compress the bitmap with JPEG format and quality 50%
bitmapImage[requestCode].compress(Bitmap.CompressFormat.JPEG,60,stream);
byte[] byteArray = stream.toByteArray();
Bitmap bitmap = BitmapFactory.decodeByteArray(byteArray,0,byteArray.length);
bitmapImage[requestCode] = Bitmap.createScaledBitmap(bitmap, bitmap.getWidth(), bitmap.getHeight(), false);
//displaying selected image to imageview
imageViews[requestCode].setImageBitmap(bitmapImage[requestCode]);
//calling the method uploadBitmap to upload image
} catch (IOException e) {
e.printStackTrace();
}
}else if(resultCode == Activity.RESULT_CANCELED) {
// User Cancelled the actiongetUriForFile
}
}

但在onActivityResult变量 fileuri 有时会得到 null，有时成功返回 URI。当我在其他手机Android 8.0.0中尝试时，没有错误。 如何解决？

java.lang.RuntimeException: Unable to resume activity {com.example.surveyonlineda/com.example.surveyonlineda.Activity.AbsenActivity}: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=100, result=-1, data=null} to activity {com.example.surveyonlineda/com.example.surveyonlineda.Activity.AbsenActivity}: java.lang.NullPointerException

Answer 1

请参阅此文档以了解您的问题，您将获得最佳解决方案

Answer 2

如我所见，fileUri没有被onActivityResult返回。您在开始cameraIntent之前创建它。因此，如果您的活动已被破坏，fileUri将为空。为了防止它，我认为您应该使用onSaveInstanceState来保存fileUri。

下面是保存字符串文件Uri的示例

@Override protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Check whether we're recreating a previously destroyed instance
if (savedInstanceState != null) {
// Restore value of fileUri from saved state
fileUri = savedInstanceState.getString(FILE_URI);
} else {
// Probably initialize values for a new instance
} 
}
@Override protected void onSaveInstanceState(Bundle savedInstanceState) {
savedInstanceState.putString(FILE_URI, fileUri);
// Always call the superclass so it can save the view hierarchy state
super.onSaveInstanceState(savedInstanceState); 
}

Answer 3

你可以试试。 它对我有用

第 1 步。创建类 GetPathFromUri.class

import android.annotation.SuppressLint;
import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.Environment;
import android.provider.DocumentsContract;
import android.provider.MediaStore;
import android.provider.OpenableColumns;
import android.util.Log;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import java.io.*;
public class GetPathFromUri {
@SuppressLint("NewApi")
public static String getPath(final Context context, final Uri uri) {
@SuppressLint("ObsoleteSdkInt") final boolean isKitKat = Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT;
// DocumentProvider
if (isKitKat && DocumentsContract.isDocumentUri(context, uri)) {
// ExternalStorageProvider
if (isExternalStorageDocument(uri)) {
final String docId = DocumentsContract.getDocumentId(uri);
final String[] split = docId.split(":");
final String type = split[0];
if ("primary".equalsIgnoreCase(type)) {
return Environment.getExternalStorageDirectory() + "/" + split[1];
}
if ("raw".equalsIgnoreCase(type)) {
return Environment.getExternalStorageDirectory() + "/" + split[1];
}
// TODO handle non-primary volumes
if ("5D68-9217".equalsIgnoreCase(type)) {
return Environment.getExternalStorageDirectory() + "/" + split[1];
}
}
// DownloadsProvider
else if (isDownloadsDocument(uri)) {
final String id = DocumentsContract.getDocumentId(uri);
if (id != null && id.startsWith("raw:")) {
return id.substring(4);
}
String[] contentUriPrefixesToTry = new String[]{
"content://downloads/public_downloads",
"content://downloads/my_downloads"
};
for (String contentUriPrefix : contentUriPrefixesToTry) {
Uri contentUri = ContentUris.withAppendedId(Uri.parse(contentUriPrefix), Long.valueOf(id));
try {
String path = getDataColumn(context, contentUri, null, null);
if (path != null) {
return path;
}
} catch (Exception e) {}
}
// path could not be retrieved using ContentResolver, therefore copy file to accessible cache using streams
String fileName = getFileName(context, uri);
File cacheDir = getDocumentCacheDir(context);
File file = generateFileName(fileName, cacheDir);
String destinationPath = null;
if (file != null) {
destinationPath = file.getAbsolutePath();
saveFileFromUri(context, uri, destinationPath);
}
return destinationPath;
}
// MediaProvider
else if (isMediaDocument(uri)) {
final String docId = DocumentsContract.getDocumentId(uri);
final String[] split = docId.split(":");
final String type = split[0];
Uri contentUri = null;
if ("image".equals(type)) {
contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
} else if ("video".equals(type)) {
contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
} else if ("audio".equals(type)) {
contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
}
final String selection = "_id=?";
final String[] selectionArgs = new String[]{split[1]};
return getDataColumn(context, contentUri, selection, selectionArgs);
}
}
// MediaStore (and general)
else if ("content".equalsIgnoreCase(uri.getScheme())) {
return getDataColumn(context, uri, null, null);
}
// File
else if ("file".equalsIgnoreCase(uri.getScheme())) {
return uri.getPath();
}
return null;
}
/**
* Get the value of the data column for this Uri. This is useful for
* MediaStore Uris, and other file-based ContentProviders.
*
* @param context       The context.
* @param uri           The Uri to query.
* @param selection     (Optional) Filter used in the query.
* @param selectionArgs (Optional) Selection arguments used in the query.
* @return The value of the _data column, which is typically a file path.
*/
private static String getDataColumn(Context context, Uri uri, String selection,
String[] selectionArgs) {
final String column = "_data";
final String[] projection = {column};
try (Cursor cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs,
null)) {
if (cursor != null && cursor.moveToFirst()) {
final int column_index = cursor.getColumnIndexOrThrow(column);
return cursor.getString(column_index);
}
}
return null;
}
/**
* @param uri The Uri to check.
* @return Whether the Uri authority is ExternalStorageProvider.
*/
private static boolean isExternalStorageDocument(Uri uri) {
return "com.android.externalstorage.documents".equals(uri.getAuthority());
}
/**
* @param uri The Uri to check.
* @return Whether the Uri authority is DownloadsProvider.
*/
private static boolean isDownloadsDocument(Uri uri) {
return "com.android.providers.downloads.documents".equals(uri.getAuthority());
}
/**
* @param uri The Uri to check.
* @return Whether the Uri authority is MediaProvider.
*/
private static boolean isMediaDocument(Uri uri) {
return "com.android.providers.media.documents".equals(uri.getAuthority());
}
public static String getFileName(@NonNull Context context, Uri uri) {
String mimeType = context.getContentResolver().getType(uri);
String filename = null;
if (mimeType == null && context != null) {
String path = getPath(context, uri);
if (path == null) {
filename = getName(uri.toString());
} else {
File file = new File(path);
filename = file.getName();
}
} else {
Cursor returnCursor = context.getContentResolver().query(uri, null,
null, null, null);
if (returnCursor != null) {
int nameIndex = returnCursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
returnCursor.moveToFirst();
filename = returnCursor.getString(nameIndex);
returnCursor.close();
}
}
return filename;
}

public static String getName(String filename) {
if (filename == null) {
return null;
}
int index = filename.lastIndexOf('/');
return filename.substring(index + 1);
}
public static File getDocumentCacheDir(@NonNull Context context) {
File dir = new File(context.getCacheDir(), DOCUMENTS_DIR);
if (!dir.exists()) {
dir.mkdirs();
}
logDir(context.getCacheDir());
logDir(dir);
return dir;
}
public static final String DOCUMENTS_DIR = "documents";
static final String TAG = "FileUtils";
private static final boolean DEBUG = false; // Set to true to enable logging
private static void logDir(File dir) {
if (!DEBUG) return;
Log.d(TAG, "Dir=" + dir);
File[] files = dir.listFiles();
for (File file : files) {
Log.d(TAG, "File=" + file.getPath());
}
}
@Nullable
public static File generateFileName(@Nullable String name, File directory) {
if (name == null) {
return null;
}
File file = new File(directory, name);
if (file.exists()) {
String fileName = name;
String extension = "";
int dotIndex = name.lastIndexOf('.');
if (dotIndex > 0) {
fileName = name.substring(0, dotIndex);
extension = name.substring(dotIndex);
}
int index = 0;
while (file.exists()) {
index++;
name = fileName + '(' + index + ')' + extension;
file = new File(directory, name);
}
}
try {
if (!file.createNewFile()) {
return null;
}
} catch (IOException e) {
Log.w(TAG, e);
return null;
}
logDir(directory);
return file;
}
private static void saveFileFromUri(Context context, Uri uri, String destinationPath) {
InputStream is = null;
BufferedOutputStream bos = null;
try {
is = context.getContentResolver().openInputStream(uri);
bos = new BufferedOutputStream(new FileOutputStream(destinationPath, false));
byte[] buf = new byte[1024];
is.read(buf);
do {
bos.write(buf);
} while (is.read(buf) != -1);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (is != null) is.close();
if (bos != null) bos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

第 2 步：

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == RESULT_OK) {
try {
String path =  GetPathFromUri.getPath(this, data.getData())
Glide.with(this).load(path).into(imageView); 
// Glide is library https://github.com/bumptech/glide
} catch (IOException e) {
e.printStackTrace();
}
}else if(resultCode == Activity.RESULT_CANCELED) {
// User Cancelled the actiongetUriForFile
}
}